Development of a Novel Nested Patch Occupancy Model Applied to River Network Data

Efforts are underway to rebuild Chinook salmon and steelhead populations in the Columbia River basin in Washington through hatchery and habitat-restoration programs. To assist with these recovery efforts, groups have been tagging and tracking millions of salmon and steelhead through the elaborate Pacific Northwest river system, with a technology similar to pet microchipping, known in science circles as passive integrated transponder (PIT) tags. This project seeks to “get more” from existing PIT-tagging data, using advanced mathematical and statistical methods. The goals include being able to improve methods for modeling fish movement patterns through river systems and for estimating the numbers of fish returning to specific river areas. This type of information will help scientists identify, or further verify, habitat areas that should be prioritized for restoration. Other benefits of the project include being able to potentially optimize the deployment of in-river fish detection stations – to lower project costs and reduce the number of fish that need to be implanted with tags. This would have the added benefit of reducing tagging-related fish mortalities. Though the model is being applied to salmon and steelhead in the Columbia River basin, the method under development may be adapted to other species in other river systems.